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1. Field of the Invention
The present invention is generally related to the meat processing industry and is specifically related to an apparatus and method for determining the source of and controlling variations in comminuted meat products.
2. Discussion of the Prior Art
The meat processing industry is regulated by the U.S. Department of Agriculture (USDA) on the basis of the chemical analysis of finished products which are marketed to the consumer. Sample lots of products are drawn on a periodic basis by USDA inspectors for chemical analysis to verify compliance with the quality control regulations. Usually, such sampling will actually be done by the meat processing company laboratory after having been certified for accuracy by the USDA.
If a meat product analysis indicates a lack of compliance to the standards, the inspector will denote the entire lot of the meat products as being "retained" which means not only that that "lot" must be reworked and cannot be shipped, but that there will be a tightened inspection in the future. Because of the cost associated with a "retained" lot, meat processors are careful to target their final product content so that violations of the USDA requirements are relatively small.
Meat processing is subject to numerous sources of variation, not found in other industries, making the problem of product consistency quite difficult. Raw meat trimmings are sold to meat processors based upon the fat content and incoming lots are routinely analyzed by the meat processor to check for the supplier's contractual compliance. Variations of fat content within .+-.2% of standard are considered acceptable, although this criteria is normally applied on the high fat side. The USDA also regulates "USDA Added Water" which is defined by the USDA as "moisture -4.times.protein." Regulation of processed meat products such as sausage, e.g., franks, bologna, luncheon meats, etc., is based upon maximum limits on the fat and "USDA Added Water" content of the consumer product.
Raw meat materials are typically blended together in a partial batch called a "preblend" or an "uncorrected" blend, which is then sampled and chemically analyzed. Based upon the analysis, the remaining material is added in adjusted amounts to "correct" the preblend to the target specification which may be a slightly conservative version of the USDA regulations governing the particular meat products. The adjusted "final" or "corrected" blend is then comminuted and passed to the stuffing department, where it is injected into casings. The product is then cooked, cooled, casings removed and packaged for shipping.
Meat processors normally conduct their own quality assurance testing to provide advance notice of possible regulatory noncompliance. Such testing normally involves chemical analysis of sampled lots for moisture, fat, protein and USDA Added Water (USDA AW). The principal sources in variation in finished product analyses result from three sources at the meat processing company. First, there is a variation in composition of the final blend or "emulsion" related to the actual blending step. Other variations in "emulsion" analysis may result from improper material use or weights, errors in assumed raw meat analysis, laboratory errors in the preblend analysis, if performed, etc.
Secondly, there are variations due to moisture loss during the cooking and holding times (this moisture loss is commonly called "shrinkage"). Additional "shrinkage" variations occur in moisture shrink loss resulting from improper smokehouse loading or schedules, faulty smokehouse equipment, abnormal holding times, etc. Thirdly, a variation is introduced in the imprecision of the laboratory analysis for moisture, fat and protein.
The laboratory analysis error can be particularly critical since protein analysis is weighted by a factor of 4 in the definition of the USDA AW. Minor variations in the protein analysis can result from insufficient mixing or comminution of the laboratory sample, the very small test weights utilized (typically 2 grams for the protein test) and variations between personnel, improper times of digestion, extraction or distillation.
Because of the large number of sources of variations encountered in meat processing, it is difficult to identify and remove assignable causes of product variation. As a result, processors must reduce their fat and USDA AW targets to provide a statistical margin of error to avoid any significant retainage. This conservative estimate of fat and USDA AW target specifications results in a "giveaway" in product analysis resulting in a 1-5% increased product cost. Therefore, it can be seen that the ability to provide product closer to a 1% cost rather than a 5% cost results in a significant cost savings and increased profit to the meat processor.
It is therefore extremely desirable in the meat processing industry to have reasonable estimates on the sizes of these three principal sources of variation in finished product analysis so that active correction action may be taken to reduce and control them. Obviously, a reduction in product chemical variability immediately results in a reduced cost of production by reducing the amount of the "giveaway." An estimation of the sizes of the three principal sources of product variation allows quick troubleshooting of problems so as to correct the area of production, i.e., blending, postblending or laboratory.
In the past, estimation of the blending variation could only be done by actual sampling and chemical analysis of samples of the final blend of meat, preferably after final comminution before stuffing into casings. The between-lots standard deviations of moisture and fat for the same product target specifications measure and provide an indication of the "uncorrected" blend variation. However, obtaining this extra sampling and analysis results in significant additional costs being incurred for this process monitoring.
In the past there has been no accepted method for determination of overall product moisture loss ("shrinkage") from the stuffing phase to the final packaging phase. The common practice has been to measure and monitor the principal component of shrink loss, that due to cooking, by weighing racked products in and out of the smokehouse. These measurements have many sources of error which limit their use for process control and include: difficulty and expense of taring (the initial zero weighing process of the racks) and identifying the racks accurately; inadvertent movement of the product from tared racks to others; loss of spray coatings of smoke treatments (which result in apparent shrinkage); lack of care by plant personnel in weighing in a busy production environment, etc. Also significant is a lack of measurement of the pre-cook and post-cook shrinkages, which can amount to several percent and can vary from batch-to-batch due to differences in holding times, etc.
Errors in the finished product laboratory analyses are difficult to detect and measure. Because of the unique lot analyses, the perishable and changeable nature of the products, small lab sample sizes, etc., it is difficult to reproduce the exact condition of a test in two different laboratories. Although laboratories may be "certified" by comparative studies with the USDA and standard methods of analysis are used, it is notorious in the industry that values obtained by the USDA laboratories, or even by outside testing laboratories, cannot in general be trusted as a definitive measure of the "true" analysis.
As a consequence, meat processing companies generally have no good idea of the exact precision and accuracy of its own laboratory. Some companies will validate their results by a between-methods comparison of moisture or fat values obtained by two different instruments or techniques. However, the effectiveness of such tests varies with the type of sample and product and generally the process of determining precision of this method is too burdensome to carry out for each and every product. It should be noted that the protein measurement analysis is particularly critical and there is currently only one accepted standard method for protein analysis. Therefore, with this measurement a "between-methods" measurement of precision cannot be attempted.